The invention relates to a lubricant carrier salt to facilitate the cold forming of workpieces of iron or steel, based on boric acid and/or alkali borate, and to a method of facilitating the cold forming of workpieces of iron or steel with the aid of this lubricant carrier salt.
It is known to facilitate the cold forming of metal workpieces by the use of fatty acid salts (soaps). These are often applied in the form of a hot, aqueous soap solution to the workpiece that is to be formed. In many cases, especially when severe forming operations are to be performed, a chemical coating is applied to the metal surface before the application of the lubricant, namely a phosphate, oxide, oxalate or sulfide coating, for example. In both cases, i.e., in the application of the lubricant to the clean workpiece or to the workpiece previously provided with a chemical coating, the lubricant is to form a uniform film which will constitute a good parting layer between the workpiece and the tool during the forming treatment.
In addition to the application of soaps to clean workpieces or workpieces previously provided with a conversion coating, it is also known to use lubricants to facilitate cold forming, which are a mixture of fatty acid salts and alkali pyrophosphate and/or alkali tetraborate (DE-A-1 594 512). Part of the soaps are to be fatty acid salts of lithium, potassium, ammonium, calcium, magnesium, zinc and/or aluminum.
Also lubricants are known which consist of neutral fat and/or oil, alkali metal soaps, and alkali metal salt of boric acid (DE-B-23 30 806), contain alkali borate, alkali sulfate and silicate, as well as chloride (GB 1561 836), or else have a content of watersoluble metal soap, alkali metal chloride, alkali metal sulfate and alkali metal borate (GB-A-2 003 923).
It is furthermore known to apply to a metal workpiece a so-called lubricant carrier salt, which does not itself act as a lubricant, but is subjected to an after-treatment, e.g., by application of soap on the drawing machine. Examples of such lubricant carrier salts are lime (Ca(OH).sub.2), iron hydroxide (Fe(OH).sub.2), and borax (Na.sub.2 B.sub.4 O.sub.7.10 H.sub.2 O) (D. Oppen, "Chemisehe Oberfl achenbehandlung als Mittel zur Erleichterung der Kaltumformung," Metalloberflfiche (1982), pages 566 ff).
Especially borax permits a high drawing speed, but its hygroscopicity is a disadvantage, so that the drawing quality of the wire, for example, decreases and rusting can be found on the wire surface. The loss of drawing quality is caused by the loss of adhesion connected with the increasing moisture absorption. Another problem lies in the drying that follows. If, for example, the wire is overdried, i.e., if the water of crystallization is wholly or even partially driven out of the applied borax, the borax coating loses its adhesion to the wire. The drawing quality is thus no longer good.